Sonic levitation apparatus

ABSTRACT

A sonic levitation apparatus (A) is disclosed which includes a sonic transducer (14) which generates acoustical energy responsive to the level of an electrical amplifier (16). A duct (B) communicates with an acoustical chamber (18) to deliver an oscillatory motion of air to a plenum section (C) which contains a collimated hole structure (D) having a plurality of parallel orifices (10). The collimated hole structure converts the motion of the air to a pulsed, unidirectional stream providing enough force to levitate a material specimen (S).

ORIGIN OF THE INVENTION

The invention described herein was made in the performance of work undera NASA contract and is subject to the provisions of Section 305 of theNational Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat.435; 42 USC 2457).

BACKGROUND OF THE INVENTION

The invention relates to a levitation microfurnace apparatus forprocessing and shaping small bodies where contact with foreign objectsor supports could be deleterious. In particular, the invention hasapplication to the processing of minute glass microballoons ormicrospheres. The microballoon is a thin wall glass structure such asused in the processing fuel in laser fusion. The microballoon is filledwith heavy hydrogen cryogenically condensed as a thin layer on theinterior of the walls. It is then bombarded with energy focused from alaser. The glass material then vaporizes and the hydrogen containedtherein is driven to the center by inertial reaction and compressed to avery dense and very hot plasma material resulting in fusion of thehydrogen.

Glass microballoons (GMBs) which are used to contain the fuel must beprecisely spherical and have uniform wall thickness. Those obtainablecommercially are only rarely of the required degree of perfection.Sorting them out from the accompanying imperfect GMBs is a major task.

It is thought that the imperfect GMBs might be brought to any degree ofgeometric perfection by remelting, reprocessing and recooling, all thetime maintaining them in a levitated state, out of contact with solid orliquid objects. Alternatively, this containerless type of processingmight be applied to the initial formation of GMBs from porous glass fritor other suitable precursor materials, as well as to their reprocessing.

Accordingly, apparatus for levitating the microballoons in amicrofurnace so that their formation may be accurately controlled toprovide a more perfectly and uniformly formed balloon is a problem towhich considerable attention need be given.

In order to form GMBs of large diameters such as up to one centimeter,it is necessary to process them in a low or zero gravity condition suchas in space. While apparatus is well known for levitating a specimen ofmaterial in a gravitational field by opposed field gradients ofelectromagnetic, acoustic or gas inertial origin, these apparatus arenot entirely suitable for levitating a microsphere in a low gravityenvironment, where accelerations are typically variable, not only withrespect to magnitude but direction as well. When positioning andlevitation of a GMB in an orthogonal triaxial coordinate system isnecessary such as in processing the GMB in space, the problem of rapidand accurate control of restoring forces to neutralize unwantedextraneous accelerations becomes particularly acute.

One well known method of levitation involves a collimated flow of anumber of equispaced equivelocity streams of gas or liquid impingingupon a GMB or other small body in such a way as to counter andneutralize the net force vector tending to displace the body from apreferred position. The device whence these streams issue is commonlycalled a collimated hole structure (CHS). The depth of the CHS holes inrelation to their diameter, their aspect ratio, influences thepersistence of the collimation and other levitating properties of theissuing streams. The higher the aspect ratio the greater thepersistence.

Due to the fact that the holes have been formed heretofore by drilling,they have been of limited aspect ratio as well as being circular.

A need also exists for apparatus for preparing solid particles ofmaterials such as novel glasses under conditions enabling a quick quenchand avoiding contact with a container.

SUMMARY OF THE INVENTION

Accordingly, an important object of the present invention is to provideapparatus for levitating a GMB or other small object which is simple yetreliable and sufficiently precise for levitating and processing a GMB ina low gravity environment.

Another important object of the present invention is to provide a simplemethod of fabricating high aspect ratio collimated hole structures (CHS)for producing levitating flows of parallel, equispaced, equivelocitystreams of gas or liquids.

Another important object of the present invention is to provide withoutthe use of valves or other moving parts, a simple means of convertingsonic energy into pulsed unidirectional flows of gases or other fluidswhich may be suitable for levitation of GMBs or other small bodies.

Yet another important object of the present invention is to provide asonic powered levitation device wherein levitation is achieved byaerodynamic lift imparted to a small body specimen from a pulsatinggaseous flow produced by passage of sonic energy through the gas withina CHS, which eliminates the need for moving valve parts.

Still another important object of the present invention is to provide asonic levitator which may be used along the axes of an orthogonaltriaxial coordinate system to levitate a body of material in a variablelow gravity environment.

It has been found according to the present invention, that the sonicoutput of a sound generator ducted into a collimated hole structure willprovide, above the free end, sufficient net air flow in one direction tolevitate a GMB or other small body. The CHS, comprising an array ofparallel passages, is carried adjacent to the end of a tubular ductwhich is connected to a chamber of the sonic energy generator. The sonicenergy generator is driven by a sinusoidal or other periodic pressuresource. The CHS behaves as a rectifier of the oscillatory sound energy,converting it into a pulsating gas flow in one direction only which isuseful in levitation. Between the sound generator and the free or uppersurface of the CHS the gas undergoes no net movement, only theoscillatory motion typical of sound transmission. Above the free surfaceof the CHS, the outward and inward swings of each sound vibration becomedifferentiated with respect to direction. The inward swings arecharacterized as omnidirectional, moving toward the CHS openings more orless symmetrically from all available direction of the 2π steradiansabove the CHS surface. The outward swings, by contrast, areunidirectional and aligned with the CHS passages. The oscillatory soniccharacter of the gas at the CHS surface gradually gives way to pulsedunidirectional flow with height, the transition being virtually completeat an elevation about a plenum diameter above the CHS surface. Thetransition is due to the fact that the outward swings being aligned andof constant cross-section are of constant flux density with height abovethe CHS while the flux density of the inward swings attenuate with theexpanding cross-section characteristic of their radial flow pattern. Inessence, during each sound vibration the sonic pump brings in air orother fluid from all directions surrounding the mouth of the CHS andejects it in one direction only.

It has also been found according to the present invention that thecross-section of the holes in a CHS need not be circular and,consequently, that CHSs of any aspect ratio desired may be madeconsisting of the interstices in a tight, regular bundle of equal lengthuniform diameter wires. The bundling may be either a hexagonal closepacked or a rectilinear array.

The sonic generator may be driven by any conventional amplifier.Levitation is initiated by simply raising the power of the amplifierwith the GMB or microsphere resting on the surface of the collimatedhole structure. As the power is increased, the microsphere first hopsaround in response to the oscillatory flow character at the surface.Eventually, it will hop high enough to attain a level where theunidirectional flow is dominant whereupon it will become stablylevitated.

BRIEF DESCRIPTION OF THE DRAWINGS

The construction designed to carry out the invention will be hereinafterdescribed, together with other features thereof.

The invention will be more readily understood from a reading of thefollowing specification and by reference to the accompanying drawingsforming a part thereof, wherein an example of the invention is shown andwherein:

FIG. 1 is a schematic view illustrating a sonic pump levitatorconstructed according to the present invention;

FIG. 2 is an enlarged top plan view of the collimated hole structure forlevitating a microsphere as illustrated in FIG. 1; and

FIG. 3 is a schematic view of the axial arrangement of six acousticallevitator devices constructed in accordance with the present inventionas arranged along the axes of a triaxial orthogonal coordinate systemfor levitating a microsphere in a stable levitating position under lowgravity conditions.

DESCRIPTION OF A PREFERRED EMBODIMENT

The drawing illustrates a sonic pump levitation apparatus for levitatinga microsphere which includes a sonic generator, designated generally asA, having an acoustical chamber in which a sound energy transportingfluid is contained. A closure means seals the chamber from the outsideenvironment and includes a medial opening which communicates with atubular duct means B which terminates in a free end. Means for drivingthe sound generator and producing a periodic pressure source is providedby an electrical power source. A plenum means C is carried adjacent thefree end of the tubular duct and includes an interstitial collimatedhole structure D within plenum C by means of which sonic energyimpressed upon the air or fluid within said structure D is converted atand above the free end into a unidirectional pulsed stream of airsuitable for levitation. The inward stroke of each sound cycle draws airor fluid into the mouth of said structure D from all angles of bearingand azimuth. This ingested air or fluid when expelled during the outwardstroke, however, is carried by its momentum in alignment with the axisof said structure D and does not laterally disperse, thus creating aunidirectional pulsating jet suitable for levitation.

As illustrated, the collimated structure D includes a plurality ofparallel passages 10 formed in a plenum 12 which is carried adjacent thefree end of the duct means B. As can best be seen in FIG. 2, thecollimated passages are comprised of the interstices between and among afour by four matrix of uniform diameter rods snugly fitted within theplenum in rectilinear array. There are nine full size interstitialpassages of quatrefoil cross-section located centrally. At theboundaries with the plenum there are twelve half size and four quartersize further passages all with trefoil cross-sections. The trefoilscontribute little to the levitating flow because of their smallereffective diameters. Circular cross-section collimated passages are wellknown and may also be used, of course.

Sound generator A may include a conventional sonic transducer device 14which may be any suitable audio loudspeaker for converting electricalenergy into sound energy. A power source is illustrated at 16 fordriving the sonic transducer 14 which may be any suitable electricalamplifier. By varying the level of the amplifier 16, the electricalenergy driving the loudspeaker 14 may be varied to vary the sonic energyand the flow momentum of the pulsed levitational stream as required.

The loudspeaker device 14 includes an acoustical chamber 18 in which asound energy transporting medium or fluid such as air is contained.

Closure means for sealing the acoustical chamber includes a flat plate19 sealed to the loudspeaker at its edges 20 and perforated at 22 toprovide communicating into the acoustical chamber 18.

The cross-section of said member 24 is square as a matter of conveniencealthough it could be circular, hexagonal or other compact closed shapeoffering minimal resistance to flow. The upper or free end of member 24serves as the plenum housing the interstitial collimated hole structure,its square cross-section nicely accommodating the rectilinear array ofinterstitial forming rods. Any slack between the rod matrix and theinterior of the plenum is taken up by appropriately sized shim stock(not shown in FIG. 2) to achieve a snug fit. Alternatively, instead oftubing, the plenum may be formed between mating blocks, a rectangulargroove being machined in one of them to just accommodate the rods andprovide a snug fit when the blocks are bolted together. The matrix mayalso be made up of a bundle or wires of fibers.

Sound generation by the loudspeaker 14 results in a correspondingsinuously reversing flow in the duct means B. At the mouth of thecollimated hole structure D are two entirely different flow patterns forthe fluxes in and out of the orifices 10 of the collimated holestructure. The influx pattern is nearly isotropic and the efflux,although pulsating, is in one direction only and in other respectssimilar to the desired collimated flow resulting from a constantpressure supply of gas through the collimated hole structure.

The dichotomous flow pattern stems from the fact that the influx isdictated by pressure gradient and the efflux by momentum of the gas. Thecollimated hole structure orifices behave as a gas sink during theinflux. Since no momentum bias is involved, a more or less isotropicsystem of isobars and pressure gradients develops, directing the flowaccordingly. Inherent in the efflux, however, is the momentum engenderedin the air during its flow through the collimated hole structure D.These momentum vectors are not soon dissipated and they dominate forsome distance above the collimated hole structure, thereby maintainingalignment of the flow with the collimated hole structure axis, andprecluding radial diversion analogous to the radial converging patternof the influx.

The inertia of the loudspeaker cone is such that the response times areeasily obtainable with an off-the-shelf loudspeaker item of modest costand high reliability. Furthermore, the output of the air stream is amonotonic and sensitive function of the incoming electrical energy orsignal to the loudspeaker.

While the sonic pump levitation apparatus resembles some fluidic devicesin its switching of gas flow patterns, this is accomplished without anyreliance upon conventional valving mechanism or vanes or, indeed anymoving part except the vibrating loudspeaker cone itself. The apparatusprovides a simple and unique means for converting an alternating gasflow into a pulsating direct current flow, to use the electrical idiom.This pulsating DC flow is capable of levitating suitably sized bodiessuch as glass microballoons and solid microspheres.

The intensity of the acoustical generator, and hence the height oflevitation is easily and rapidly controlled by adjustment of theelectrical power to the loudspeaker. Response time is of the order ofthe reciprocal of the upper frequency limit of the speaker. The glassmicroballoons are of the order of a millimeter in diameter. Under theseconditions, power levels of about a quarter of a watt produce stablelevitation. Except in the region immediately above the collimated holestructure plenum, stability is comparable to that obtained with thesteady flow of levitation gas. This region of instability, which extendsfor about a diameter of the plenum above the surface of the collimatedhole structure, coincides with the cross-over of the influx and effluxflow patterns.

The high aspect ratio of the passages of the collimated hole structureand the relatively long distance between the collimated hole structureplenum to the loudspeaker thermally isolate the levitation flow from allelements of the apparatus in back of the plenum. Thermally sensitivecomponents such as the loudspeaker thus may be safely incorporated withhigh temperature levitating conditions.

EXAMPLE

In one embodiment, a four-inch ten watt loudspeaker was utilized togenerate enough air flow in one direction to levitate a solid sixhundred micron glass microsphere. The face of the speaker was coveredwith a flat steel plate 1/8 of an inch thick and a duct B was madeutilizing a 1/4 inch square tubing approximately 2.75 inches long. Thecollimated hole structure D was contained in a plenum means 12 and wascomprised of the interstices 10 in a square array of 16 equal lengths,equal diameter rods held in place by the clamping action of suitablysized shims (not shown) inserted along the adjacent sides of plenummeans 12. The length of the interstitial passages is 0.5 inches. The roddiameter was 0.025 inches, hence the passage diameter varied from amaximum of 0.025 to a minimum of 0.010 inches. The aspect ratio of thepassages is defined as the ratio of their length to diameter, and ispreferably in the range of 5:1 to 50:1.

Levitation was initiated by resting the glass microsphere on the surfaceof the collimated hole structure and raising the level of the powertransmitted by amplifier 16. As the power was increased, the glassmicrosphere first bobbed around the surface of the collimated holestructure and then leaped up to around a millimeter from the surface andlocked into a stable levitation position. Once levitated, the glassmicrosphere could be raised and lowered over a range of severalmillimeters by adjusting the power fed to the loudspeaker 14. Levitationwas accomplished utilizing the four inch ten watt loudspeaker operatedin a range of approximately 750 hertz.

As illustrated in FIG. 3, six sonic levitation apparatus A areillustrated with the members of each of three pairs being arranged inopposition along an axis of a triaxial orthogonal coordinance system. Inthis manner, the microsphere or microballoon S may be levitated in astable position when undergoing processing in low gravity environmentssuch as in space. In this case, a conventional computer ormicroprocessor 30 may be utilized in conjunction with a conventionalvideo scanner 32 of the specimen S to maintain the positioning of themicrosphere or microballoon through feedback control of the energy levelof amplifier 16 and loudspeaker 14 of each sonic pump device.

Deviations in the levitation position of the microsphere S can bedetected by the video scanner and input to the computer. The computerthen generates an electrical signal from the feedback loop whichcorrects the levitational position by increasing or decreasing the powerfed to a loudspeaker and thus correcting the gas pulses from thelevitational apparatus as required. Since the gas pulse must have veryrapid up and down times, on the order of a milisecond, apparatus of thepresent invention is particularly advantageous since there are no movingparts. Valve systems have very high inertia and not very rapid responsetimes. In accordance with the present invention, the apparatus disclosedherein has very rapid response times and is very readily usable in suchan automatic system.

While a preferred embodiment of the invention has been described usingspecific terms, such description is for illustrative purposes only, andit is to be understood that changes and variations may be made withoutdeparting from the spirit or scope of the following claims.

What is claimed is:
 1. Apparatus for levitating a material specimencomprising:a duct having an interior adapted to be filled with gas; acollimated passage means disposed within and at an end of said duct,said collimated passage means including an array of parallel passagewayscommunicating with the interior of said duct with the surroundingatmosphere; and a sound generator means for imparting oscillatory motionto the gas within said duct so as to provide levitating force in theform of pulsed, unidirectional motion of gas axially beyond the end ofsaid collimated passage means.
 2. The apparatus of claim 1 including anacoustical chamber in communication with the interior of said duct. 3.The apparatus of claim 2 wherein said duct is disposed vertically. 4.The apparatus of claim 3 wherein said acoustical chamber is joined tothe lower end of said duct and sealed from the outside environment. 5.The apparatus of claim 4 wherein said sound generator means includes adevice for converting electrical energy into acoustical energy.
 6. Theapparatus of claim 5 including a variable power source of electricalenergy connected to said sound generator means for controllably varyingsaid acoustical energy and the levitational forces produced thereby. 7.The apparatus of claim 6 including a plurality of solid rod, wires orfibers of circular cross-section disposed vertically in a bundle withina plenum region forming the upper end of said duct, the open spacesbetween the said rods, wires or fibers providing an array of parallelpassageways.
 8. The apparatus of claim 6 wherein said duct is a tube ofgenerally rectangular cross-section.
 9. The apparatus of claim 8 whereinthe ratio of length to diameter of said rods is in the range of 5:1 to50:1.
 10. The apparatus of claim 9 wherein the length of said rods isabout 0.5 inch and their diameter 0.025 inch.
 11. The apparatus of claim6 wherein said acoustical chamber is contained in an upwardly extending,conical-shaped speaker having its upper periphery sealed to a flatplate.
 12. The apparatus of claim 11 wherein said plate is penetrated bya central passageway axially above the center of said speaker, the saidplate being sealed to the lower end of said duct around the periphery ofsaid plate passageway.
 13. An apparatus for providing a pulsed,unidirectional gas flow comprising:a tubular duct adapted to be filledwith gas; a collimated passageway structure disposed within and at anend of said duct, said structure having an array of parallel passagewayscommunicating the interior of said duct with the surroundingenvironment; a sound generator means for imparting oscillatory motion tothe gas within said duct, thereby providing a pattern of pulsed,unidirectional gas flow at a zone located beyond the outer end of saidpassageway structure.
 14. The apparatus of claim 13 wherein said soundgenerator means comprises a conical speaker disposed in axial alignmentwith said duct.
 15. The apparatus of claim 14 including a flat platesealed to the extended end of said speaker and penetrated by apassageway communicating the acoustical chamber contained therein withthe inerior of said duct.
 16. The apparatus of claim 15 wherein saidcollimated passageway structure comprises a plurality of rods ofcircular cross-section and uniform diameter disposed in axial alignmentso as to provide axially extending open spaces therebetween. 17.Apparatus for levitating a material specimen in a low orvariable-gravity environment comprising:a plurality of tubular ductsarranged in opposed pairs in a triaxial orthogonal coordinance system,each of said ducts having an interior adapted to be filled with gas andcontaining at one end a collimated passage means including an array ofparallel passageways communicating with the interior of the duct withthe surrounding atmosphere and at its other end a sound generator meansfor imparting oscillatory motion to the gas within the duct so as toprovide levitating force in the form of pulsed unidirectional motion ofgas axially beyond said collimated passage means; and means for variablysupplying energy to said sound generator means.
 18. The apparatus ofclaim 17 including means for sensing the position of a specimenlevitated therein and controllably adjusting the energy supplied to saidsound generator means so as to maintain said specimen at a predeterminedlocation.
 19. The apparatus of claim 18 wherein said sound generatormeans is a loudspeaker.
 20. The apparatus of claim 19 wherein saidsensing means is a video scanner.